Devices for determining the earth's magnetic field have long been known in the form of compasses. These normally utilized a point-journalled magnetic needle which adjusts to the north/south direction of the magnetic field and is relatively difficult to read.
More sophisticated compass equipment itilizes electromagnetic sensors comprising different types of solenoids to which electric voltages are applied and which are intended to deliver measuring signals to indicating or reading instruments. Such equipment is used, for instance, as an aid in manoeuvring water-borne vessels and aircraft, and the relatively complicated design of such equipment renders it very expensive.
Such equipment is used, for instance, as an aid in maneuvering water-borne vessels and aircraft, and the relatively complicated design of such equipment renders it very expensive. Such an equipment is described in U.S. Pat. No. 4,503,621 (Fowler) where solid state flux gates are supported on a platform gimballed to maintain a substantially horizontal orientation. Such a flux gate comprises coil means and a magnetically saturable core of so-called Wiegand type.
Magnetic field sensors comprising magnetic elements of Wiegand type are described e.g. in U.S. Pat. No. 4,639,670 (Norman). The drawback in using such an element is among others that it has to be reset after every pulse generated by the magnetic field sensed as discussed in U.S. Pat. No. 4,639,670. Therefore, the control and detection circuits are rather complex.
Another drawback in existing solid state compass and other magnetic field sensor equipment is the use of digital time or frequency measuring for having a value of the magnetic field sought for. Besides the patents mentioned above such a time or frequency measuring method is used for an electronic digital compass described in U.S. Pat. No. 4,918,824 (Farrar) issued Apr. 24, 1990. As is quite clear from this patent, for example shown in FIG. 19, the electronic circuits being used are complex and it is necessary to use two detector coils for every detector core. Though making use of an amorphous reentrant wire core Farrar has not understood to take advantage of the properties of this core material but only replaced the Wiegand core used in the magnetic field detectors of prior art. This means an undesirable waste of energy which can be seen in FIGS. 13 through 16 where the graphs show a drive signal having a large amplitude.